Kernel: Simplify VFS::resolve_path() further

It turns out we don't even need to store the whole custody chain, as we only
ever access its last element. So we can just store one custody. This also fixes
a performance FIXME :^)

Also, rename parent_custody to out_parent.

Kernel/FileSystem/VirtualFileSystem.cpp

@@ -675,7 +675,7 @@ Custody& VFS::root_custody()
     return *m_root_custody;
 }
 
-KResultOr<NonnullRefPtr<Custody>> VFS::resolve_path(StringView path, Custody& base, RefPtr<Custody>* parent_custody, int options, int symlink_recursion_level)
+KResultOr<NonnullRefPtr<Custody>> VFS::resolve_path(StringView path, Custody& base, RefPtr<Custody>* out_parent, int options, int symlink_recursion_level)
 {
     if (symlink_recursion_level >= symlink_recursion_limit)
         return KResult(-ELOOP);
@@ -684,23 +684,13 @@ KResultOr<NonnullRefPtr<Custody>> VFS::resolve_path(StringView path, Custody& ba
         return KResult(-EINVAL);
 
     auto parts = path.split_view('/', true);
-
     auto& current_root = current->process().root_directory();
 
-    NonnullRefPtrVector<Custody, 32> custody_chain;
+    NonnullRefPtr<Custody> custody = path[0] == '/' ? current_root : base;
-
-    if (path[0] == '/') {
-        custody_chain.append(current_root);
-    } else {
-        for (auto* custody = &base; custody; custody = custody->parent()) {
-            // FIXME: Prepending here is not efficient! Fix this.
-            custody_chain.prepend(*custody);
-        }
-    }
 
     for (int i = 0; i < parts.size(); ++i) {
-        auto& current_parent = custody_chain.last();
+        Custody& parent = custody;
-        auto parent_metadata = current_parent.inode().metadata();
+        auto parent_metadata = parent.inode().metadata();
         if (!parent_metadata.is_directory())
             return KResult(-ENOTDIR);
         // Ensure the current user is allowed to resolve paths inside this directory.
@@ -712,27 +702,27 @@ KResultOr<NonnullRefPtr<Custody>> VFS::resolve_path(StringView path, Custody& ba
 
         if (part == "..") {
             // If we encounter a "..", take a step back, but don't go beyond the root.
-            if (custody_chain.size() > 1)
+            if (custody->parent())
-                custody_chain.take_last();
+                custody = *custody->parent();
             continue;
         } else if (part == "." || part.is_empty()) {
             continue;
         }
 
         // Okay, let's look up this part.
-        auto child_id = current_parent.inode().lookup(part);
+        auto child_id = parent.inode().lookup(part);
 
         if (!child_id.is_valid()) {
-            if (parent_custody) {
+            if (out_parent) {
                 // ENOENT with a non-null parent custody signals to caller that
                 // we found the immediate parent of the file, but the file itself
                 // does not exist yet.
-                *parent_custody = have_more_parts ? nullptr : &current_parent;
+                *out_parent = have_more_parts ? nullptr : &parent;
             }
             return KResult(-ENOENT);
         }
 
-        int mount_flags_for_child = current_parent.mount_flags();
+        int mount_flags_for_child = parent.mount_flags();
         // See if there's something mounted on the child; in that case
         // we would need to return the guest inode, not the host inode.
         if (auto mount = find_mount_for_host(child_id)) {
@@ -742,7 +732,7 @@ KResultOr<NonnullRefPtr<Custody>> VFS::resolve_path(StringView path, Custody& ba
         auto child_inode = get_inode(child_id);
         ASSERT(child_inode);
 
-        custody_chain.append(Custody::create(&current_parent, part, *child_inode, mount_flags_for_child));
+        custody = Custody::create(&parent, part, *child_inode, mount_flags_for_child);
 
         if (child_inode->metadata().is_symlink()) {
             if (!have_more_parts) {
@@ -753,13 +743,13 @@ KResultOr<NonnullRefPtr<Custody>> VFS::resolve_path(StringView path, Custody& ba
             }
             auto symlink_contents = child_inode->read_entire();
             if (!symlink_contents) {
-                if (parent_custody)
+                if (out_parent)
-                    *parent_custody = nullptr;
+                    *out_parent = nullptr;
                 return KResult(-ENOENT);
             }
 
             auto symlink_path = StringView(symlink_contents.data(), symlink_contents.size());
-            auto symlink_target = resolve_path(symlink_path, current_parent, parent_custody, options, symlink_recursion_level + 1);
+            auto symlink_target = resolve_path(symlink_path, parent, out_parent, options, symlink_recursion_level + 1);
 
             if (symlink_target.is_error() || !have_more_parts)
                 return symlink_target;
@@ -771,11 +761,11 @@ KResultOr<NonnullRefPtr<Custody>> VFS::resolve_path(StringView path, Custody& ba
             remaining_path.append('.');
             remaining_path.append(path.substring_view_starting_after_substring(part));
 
-            return resolve_path(remaining_path.to_string(), *symlink_target.value(), parent_custody, options, symlink_recursion_level + 1);
+            return resolve_path(remaining_path.to_string(), *symlink_target.value(), out_parent, options, symlink_recursion_level + 1);
         }
     }
 
-    if (parent_custody)
+    if (out_parent)
-        *parent_custody = custody_chain.last().parent();
+        *out_parent = custody->parent();
-    return custody_chain.last();
+    return custody;
 }

Kernel/FileSystem/VirtualFileSystem.h

@@ -103,7 +103,7 @@ public:
     void sync();
 
     Custody& root_custody();
-    KResultOr<NonnullRefPtr<Custody>> resolve_path(StringView path, Custody& base, RefPtr<Custody>* parent = nullptr, int options = 0, int symlink_recursion_level = 0);
+    KResultOr<NonnullRefPtr<Custody>> resolve_path(StringView path, Custody& base, RefPtr<Custody>* out_parent = nullptr, int options = 0, int symlink_recursion_level = 0);
 
 private:
     friend class FileDescription;